On my drive home today, the oil pressure in my 87 TD, OM603, 190,000 miles, started acting oddly. Normally it pegs high when the engine is cold and then once the oil is warm, it drops down to 1.5-2ish at idle, and re-pegs as soon as you raise the rpm. It has regular DELO in it (15-40?) and the oil level is fine. Today, having not driven the car for 2 hours, I started the car and drove a short distance when I looked at the oil P. It was at 2, which surprised me because the engine was cool. When I sped up, it only slightly increased the P, but it mostly stuck at 2. There was no way to get 3 or pegged this afternoon. At idle, the P was 1 bar. I had to drive home to get my son, but I did so knowing I might be destroying my "new car".

As soon as I got home, I turned off the car and the P dropped to zero. I didn't think to open the hood and look for oil flow inside the filler cap, as I just wanted to turn off the engine ASAP. But when I turned the key back on, the oil pressure jumps to 1 before you even turn the starter. So something is definitely wonky (to use a technical term).

Based on my research just now, it looks like it is probably one of five things:
1) blocked oil pickup in the sump
2) malfunctioning oil pump
3) malfunctioning oil pressure sensor (sender)
4) malfunctioning oil pressure gauge on dash display
5) malfunctioning wire between the sensor and dashboard

I am hoping it is 3 as this seems the most likely and easiest to fix. 4 or 5 wouldn't be bad, and obviously I would prefer it not be either of the first two.

Based on my reading, when the sending unit fails for many of you, it pegs high. But that obviously isn't the case here. Does that suggest that my problem isn't likely to be the sender?

Once in a rare while, I would notice when I got into the car (no yet running) that there was a pressure indicated on the gauge. When I hit the starter, the pressure would drop to 0 very briefly, and then peg a few seconds later. If you get an indicated pressure when the car isn't running, does this suggest the sender or the gauge is more likely to blame?

And while unlikely to be relevant, a lot of the warning indicator lights on my dash are very dim when they are tested with the key first turned. It seems doubtful, but maybe my dash has some common problem with the lights and the oil pressure gauge. It was rainy today if grounding can ever be an issue with these things.

Would you start the car to see if this problem was a one-time electrical gremlin? Or would you replace the sender first (or install a mechanical pressure gauge) and then risk starting it up?

Any other thoughts are appreciated. Thanks for your time. And sorry about misspelling "anomalies"! ha ha.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).